On October 9, 2022, a powerful surge of gamma-ray radiation engulfed our solar system, inundating gamma-ray detectors on multiple orbiting satellites and prompting astronomers to pursue the event with the world’s most advanced telescopes.
This unprecedented occurrence, designated as GRB 221009A based on its discovery date, proved to be the most luminous gamma-ray burst (GRB) ever documented.
Published today in the Astrophysical Journal Letters, a groundbreaking study unveils new insights into the enigmatic origins of these extraordinary cosmic eruptions. Researchers analyzed data from GRB 221009A across a spectrum of wavelengths, from radio waves to gamma-rays, incorporating crucial millimeter-wave observations from the Center for Astrophysics | Harvard & Smithsonian’s Submillimeter Array (SMA) in Hawaii.
The gamma-ray emission from GRB 221009A persisted for over 300 seconds, leading astronomers to categorize it as a “long-duration” GRB. It is believed that such events signal the birth of a black hole, which occurs when the core of a massive, rapidly spinning star succumbs to its own gravitational force. This nascent black hole then propels intense jets of plasma at nearly the speed of light, piercing through the collapsing star and emitting brilliant gamma-rays.
The unprecedented brightness of GRB 221009A presented a tantalizing enigma: what would follow the initial gamma-ray burst? “As the jets collide with the gas surrounding the dying star, they generate a brilliant ‘afterglow’ that spans the entire light spectrum,” explains Tanmoy Laskar, Assistant Professor of Physics and Astronomy at the University of Utah, and the study’s lead author. “The afterglow diminishes quite swiftly, which necessitates our agility in capturing its fleeting light and the secrets it holds.”
In a coordinated effort to study GRB 221009A’s afterglow using the world’s finest radio and millimeter telescopes, astronomers Edo Berger and Yvette Cendes from the Center for Astrophysics (CfA) expeditiously collected data using the Submillimeter Array (SMA).
“This extraordinarily bright burst offered a rare opportunity to investigate the intricate behavior and evolution of an afterglow in unparalleled detail—we couldn’t let it slip away!” exclaims Edo Berger, Professor of Astronomy at Harvard University and the CfA. “Having researched these phenomena for over two decades, I can say that this event was as thrilling as the first GRB I ever observed.”
Garrett Keating, SMA Project Scientist and CfA researcher, adds, “The SMA’s rapid-response capability enabled us to swiftly direct the array towards GRB 221009A’s location. Our team was eager to observe the remarkable brightness of this GRB’s afterglow, which we continued to monitor for over 10 days as it gradually faded.”
Before GRB 221009A, some of the most significant gamma-ray bursts (GRBs) include GRB 080319B, GRB 110918A, and GRB 130427A. These GRBs stood out due to their exceptional brightness, duration, or energy release.
- GRB 080319B: Detected on March 19, 2008, this GRB was notable for its extreme brightness, briefly becoming visible to the naked eye despite being 7.5 billion light-years away. The event’s optical afterglow was the most luminous ever recorded.
- GRB 110918A: Occurring on September 18, 2011, this GRB was one of the most energetic ever observed. It released an estimated 5.4 x 10^54 ergs (5.4 x 10^47 joules) of energy and had a duration of about 500 seconds.
- GRB 130427A: Detected on April 27, 2013, this GRB was remarkable due to its relative proximity to Earth (just 3.6 billion light-years away) and its extraordinarily long duration of around 20 hours. It had a high-energy gamma-ray photon with an energy of around 95 GeV, which was the highest energy photon observed from a GRB at the time.
Gamma-ray bursts, in general, are believed to be caused by two main processes:
- Long-duration GRBs: These bursts, which typically last more than 2 seconds, are thought to result from the core-collapse of massive stars (at least 20-30 times the mass of the Sun). As the core collapses, a black hole or a neutron star is formed, and relativistic jets of material are ejected at near the speed of light. These jets interact with the surrounding medium, generating high-energy gamma-ray photons.
- Short-duration GRBs: Lasting less than 2 seconds, these bursts are believed to be caused by the merger of two compact objects, such as neutron stars or a neutron star and a black hole. The merger results in the formation of a black hole and the release of powerful jets, which emit gamma-rays.
Analysis of GRB 221009A
Upon examining and integrating data from the SMA and various telescopes worldwide, astronomers found themselves perplexed: the millimeter and radio wave measurements appeared far brighter than anticipated based on the visible and X-ray light.
“This is one of the most comprehensive datasets we have ever acquired, and it’s evident that the millimeter and radio data deviate from our expectations,” states CfA Research Associate Yvette Cendes. “A handful of GRBs in the past have displayed a transient excess of millimeter and radio emission, which is thought to indicate a shockwave within the jet itself. However, the excess emission in GRB 221009A exhibits a distinct behavior compared to previous cases.”
Cendes continues, “We may have uncovered an entirely novel mechanism for generating excess millimeter and radio waves.”
One potential explanation, according to Cendes, is that the powerful jet produced by GRB 221009A exhibits a more intricate structure than those in most GRBs. “It’s plausible that the visible and X-ray light originate from one segment of the jet, while the early millimeter and radio waves are emitted by a separate component.”
“Fortunately, the afterglow’s intensity allows us to continue monitoring its radio emission for months or even years,” adds Berger. “Over this extended period, we hope to decode the enigmatic origin of the early excess emission.”
Regardless of the precise intricacies of this specific GRB, the ability to swiftly respond to GRBs and similar events using millimeter-wave telescopes represents a crucial new capacity for astronomers.
Probing Deeper into the Early Universe
The discovery and detailed analysis of GRB 221009A not only enhances our understanding of gamma-ray bursts but also provides valuable insights into the early universe. GRBs serve as cosmic beacons, illuminating the distant reaches of the cosmos and allowing astronomers to probe the conditions and processes that occurred billions of years ago.
Furthermore, the detection of such intense gamma-ray bursts enables the study of the intergalactic medium—the diffuse gas found between galaxies. By observing the interactions between gamma-ray photons and the intergalactic medium, astronomers can glean valuable information about the distribution and composition of matter throughout the universe.
This unprecedented event also highlights the importance of international collaboration in astronomical research. The rapid response and coordination of telescopes worldwide enabled the swift collection and analysis of vital data, ultimately leading to the discovery of the possible new mechanism for generating excess millimeter and radio waves. As technology continues to advance, future discoveries will undoubtedly rely on the cooperative efforts of scientists and observatories across the globe.
The investigation of GRB 221009A has unveiled intriguing new possibilities in our understanding of gamma-ray bursts and the early universe. The event serves as a testament to the power of global collaboration in astronomy and emphasizes the need for continued research into the enigmatic phenomena that shape our cosmos.
More Information: https://pweb.cfa.harvard.edu/news/brightest-gamma-ray-burst-ever-observed-reveals-new-mysteries-cosmic-explosions